Johst studied medicine and philosophy and - later - history of art. He joined the army by his own will in 1914. In 1918 he settled down at the Starnberger See.
His early work is influenced by expressionism (e.g. Der Anfang (1917), Der König (1920)). Later he turned to the naturalism psychology (Wechsler und Händler (1923), Thomas Paine (1927)).
In 1935 Johst became the President of the Reichsschrifttumskammer and of the Deutsche Akademie für Dichtung - organisations for German writers, but at this time just for writers who were writing pro-Nazi stuff.
In the essay "Standpunkt und Fortschritt" (1933) he declared his agreement with Hitler's thoughts.